1. Field of the Invention
The present invention relates to a radiation beam conditioning system for use in a lithographic apparatus, a lithographic apparatus, and a method for manufacturing a device.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern can be transferred onto all or part of the substrate (e.g., a glass plate), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
Instead of a circuit pattern, the patterning device can be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. Lithographic apparatus designed to expose a substrate of this type can provide an exposure region that covers a full width of the rectangular substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
In lithography, it is common to provide a variety of components between a radiation source and the so-called illuminator in order to condition the beam of radiation. In particular, it is desirable to improve the radiation uniformity across the beam, reduce the speckle within the radiation beam and, in the case of a pulsed radiation source, adjust the width of a pulse, e.g., its duration, and, in some cases, the radiation dose within the pulse. In general, it is necessary to ensure that the dose of radiation received at a substrate is close to a desired level because variations in the dose have a significance impact on the so-called critical dimension (CD) uniformity. In a lithography apparatus using a mask, the control of the dose within a single pulse of radiation is typically not critical because many pulses, for example 100, may be used in order to image a part of a pattern onto a substrate. Accordingly, variations in the energy within the pulses tend to become averaged out. However, in maskless lithography, control of the energy within each pulse is more important because far fewer pulses of radiation, for example only a single pulse, are used to image each part of the pattern onto the substrate. Therefore, it has previously been proposed for maskless lithographic apparatus to provide a component that can trim each pulse of radiation, such that the total energy in each pulse of radiation is reduced to a predetermined level.
However, in all lithographic apparatus, it is necessary to avoid wastage of the radiation provided by the radiation source because the speed at which the lithographic apparatus can image a pattern on the substrate is limited by the intensity of the radiation that can be imaged onto the substrate. Accordingly, it is necessary to reduce the wastage of the radiation in order to maximize the throughput of the lithographic apparatus. However, the inclusion of a plurality of components in order to condition the beam of radiation reduces the efficiency of the system because, in general, each component will not be perfectly transmissive, and accordingly, some of the energy of the beam of radiation will be wasted as it passes through each component.
Therefore, what is needed is a system and method that permit a conditioning of a beam of radiation with minimal wastage of a beam of radiation.